In today's mobile wireless networks like the Global System for Mobile communications (GSM), the area in which transfer of radio signals between a mobile device and a selected base station is possible, can change when the device moves. A base station is a wireless communications station for providing access of mobile devices to the mobile wireless network. The area covered by a base station, or a subunit of it, is frequently referred to as a cell. In order for incoming calls to be received, the mobile device is located. This means that the system determines where the device currently is. When the mobile device is idle, i.e. switched on and not active in a call, its mobility is tracked by the system using the concept of registration areas. Often, e.g. in GSM, the location is tracked by the core network of the system. An example of the concept of registration areas are the location areas in GSM. A location area is a set of one or more cells which are grouped together to optimize signaling to and from mobile devices.
Because of geographical mobility, or due to changes in the coverage of the registration areas, mobile devices in idle mode update their registration towards the core network when they cross the border between registration areas. This process is generally referred to as registration area update or registration update procedure and it can cause excess registration traffic. Good examples are the bursts of registration traffic around the border of location areas when trains full with commuters traverse those borders. This is a serious problem e.g. in heavy populated areas or cities when big numbers of people move together due to commuting or a concert or a sports event. Users around the borders of location areas are potentially unable to have access to communication services for a certain time period due to congestion caused by a burst of registration update procedures.
Solutions for the problems occurring due to a burst of registration update procedures have been the subject of investigation from the 3rd Generation Partnership Project (3GPP) in the 3GPP Technical Report 23.880 V0.1.0 (2007-10), “Stage2 for Registration in Densely-populated area (RED); Solution Placeholder”. Different alternatives are proposed as solutions. A short summary of such solutions is mentioned below.
Mobile devices which execute a registration update receive a list of location areas. As long as the devices move within a location area in this list, they don't have to execute a new registration update. By providing different lists to different sets of mobile devices, it can be achieved that only devices from some sets generate registration signaling at a specific location area border. As an alternative, the concept of extra areas is introduced, which are defined to be smaller than location areas. Due to their smaller size reduction in the amount of paging signaling during registration area updates can be achieved. In both cases the amount of signaling between the mobile devices and the core network at location area borders can only be divided by a constant factor, still allowing significant peaks in registration signaling to remain. Also the bursts of registration traffic around the border of location areas in the case of trains full of commuters are not reduced.
Alternatively a random wait time for registration area updates can be used, thus aiming to spread the updates over a period of time when the mobile devices move to a new registration area. In this case, during the random wait time, the mobile devices are not reachable. It is difficult to find a right value for the wait time since if it is long there is a high probability of call failures. If the wait time is short the advantage of spreading the signaling load is lost.
All alternatives increase complexity and implementation costs. Due to these reasons they not attractive as general case solutions to solve the problems occurring by the burst of registration update procedures, making them only appropriate for specific areas where frequent signaling bursts justify the increased complexity and implementation costs.